17-03-2010, 01:20 PM
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PROGRAMMABLE LOGIC CONTROLLERS AND SCADA
Presented by
N. D. Ramesh
Road Map
Introduction
Basic PLC components
Introduction to STEP 7 LITE
Programming PLC and Ladder logic
Exercises
SCADA
Future scope
Introduction
A digitally operating electronic apparatus which uses a programmable memory for implementing specific functions such as :
Logic sequencing
Timing
Counting
Arithmetic control
through digital or analog
input/output modules
Purpose of PLC & its functions
Initially designed to replace relay logic boards
Accepts input from a series of switches
Sends output to devices or relays
Functions
On-off control,
Sequential control,
Feedback control, and
Motion control
Basic PLC components
Power Supply
Every PLC has an external or internal Isolated Power Supply.
Isolated Power Supplies can have more than one isolated output.
Normally Power supplies are high voltage. Typically 24 Volts for industrial PLCs.
INPUTS & Outputs
These are the physical connections from the real world to the PLC.
Inputs can be limit switches, push buttons, and sensors, anything that can "switch" a signal on or off.
Outputs are solenoids, lamps, contactors, relays etc,.
The number of DI/Os can be increased by adding additional DI/O
modules
CPU
CPU module mainly classified into three different parts based on their operation.
Processor
program memory
serial communication ports
Scan cycle of PLC
STEP 7 LITE
STEP 7 LITE
Programming PLC
FBD (Function block diagram)
LD (Ladder diagram)
ST (Structured text, similar to the Pascal programming language)
IL (Instruction list, similar to assembly language)
SFC (Sequential function chart).
Ladder logic
Ladder diagram is a language which composes program using relay symbols as a base in an image similar to a hard-wired relay sequence.
A ladder logic program has a ladder look to it. The sides of the ladder are the power rail on the left and ground rail on the right. The rungs of the ladder consists of Virtual Relay Components.
Virtual Relay components
[ ] Normally Open Switch
[/] Normally Closed Switch
( ) Coil
And many more..
Exercises
Direct online starter
Sequential switching of motors
Fan control unit
Tank level controller
Traffic light control
Bottling Plant simulation
SUPERVISORY CONTROL AND DATA ACQUISTION (SCADA)
SCADA refers to combination of telemetry and Data acquisition. It consist of:
Collecting data
Transferring it back to control site
Carrying out necessary analysis and control
Displaying data on operator screens
TELEMETRY
It is the technique used in transmitting and receiving information or data over a medium. Information can be Voltage, speed, level, temp, flow etc. Data is transmitted to another location through cables, Telephone, radio. Information may come from multiple locations.
DATA ACQUISTION
It is method used to access and control information from equipment being controlled and monitored. The data accessed is then forwarded on to a telemetry system fro transfer to different sites.
Future scope
Study of :
Interrupts
Counters
Communication Protocol:
Profibus
How to use communications to communicate with other PLC,
smart actuators and sensors etc.
